“With a jump of 6 per cent for 15- to 17-year-olds in prison over the last year alone, it is clear the current system is not working to support young people with very complex needs,” said the charity’s policy director, Kathy Evans.

“The serious step of locking up a child should only ever be a last resort which is clearly not what’s happening in our courts. With 70 per cent of the Youth Justice Board budget being spent on a rapidly increasing custody population, surely it’s time to focus on prevention and alternatives to custody.”

The latest figures reveal that 2,528 15- to 17- year olds were in custody in August 2006. This includes a significant rise in the number given immediate custodial sentences for violence against another person, robbery and burglary.

There were also 9,060 young adults aged between 18- and 20-years-old in August 2006 in prison, compared with 8,708 the previous year.